Decabromodiphenylethane (DBDPE), 1,2-bis(pentabromophenyl)ethane, is a time-proven commercial flame retardant for use in many flammable macromolecular materials, e.g. thermoplastics, thermosets, cellulosic materials and back coating applications.
Among prior processes for effecting bromination of diphenylethane (DPE) are those described in U.S. Pat. Nos. 5,457,248; 6,518,468; 6,958,423; 6,603,049; 6,768,033; and 6,974,887. The catalysts of choice in conducting such brominations are aluminum catalysts such as aluminum powder and aluminum trihalides in which the halogen is chlorine and/or bromine, and iron catalysts such as iron powder or iron trihalides in which the halogen is chlorine and/or bromine.
While the bromination process can be conducted in various ways, it is desirable to carry out the process in an excess of liquid bromine as the reactant and reaction medium. In such processes, a substantial portion of the major coproduct of the reaction, gaseous hydrogen bromide contains bromine in the vapor state. In order to recover the bromine for reuse, it is necessary to separate the bromine from the gaseous hydrogen bromide. Also, since anhydrous hydrogen bromide is commercially useful as a reactant for producing other chemical products, the removal of bromine from the gaseous hydrogen bromide provides anhydrous hydrogen bromide of sufficient purity for such commercial uses.
Heretofore, gaseous mixtures of bromine and hydrogen bromide have been fed to diphenyl oxide whereby partially brominated diphenyl oxide is formed. This reaction proceeds readily in the absence of a catalyst when using less than 2 moles of bromine per mole of diphenyl oxide.